Mirror driving device and driving method thereof

ABSTRACT

A piezoelectric actuator part which generates a driving force to rotate a mirror part about a rotation axis includes a first actuator part and a second actuator part having a both-end supported beam structure in which base end parts on both sides in an axial direction of the rotation axis are fixed. The first actuator part has a first electrode part and second electrode parts. The second actuator part has third electrode parts and a fourth electrode part. The arrangement of the each electrode part constituting an upper electrode corresponds to a stress distribution of principal stresses in a piezoelectric body during resonance mode vibration, and a piezoelectric portion corresponding to positions of the first electrode part and the third electrode parts and a piezoelectric portion corresponding to positions of the second electrode parts and the fourth electrode part generate stresses in opposite directions.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of PCT InternationalApplication No. PCT/JP2015/077589 filed on Sep. 29, 2015 claimingpriority under 35 U.S.C §119(a) to Japanese Patent Application No.2014-201651 filed on Sep. 30, 2014. Each of the above applications ishereby expressly incorporated by reference, in their entirety, into thepresent application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mirror driving device and a drivingmethod thereof, and more particularly to a structure of a micromirrordevice suitable for an optical deflector used for optical scanning and adriving method thereof.

2. Description of the Related Art

A microscanner fabricated using a silicon (Si) microfabricationtechnology (hereinafter referred to as “microelectromechanical system(MEMS) scanner”) is characterized by its small size and low powerconsumption, and is thus expected to be widely used in applicationsranging from a laser projector to an optical diagnostic scanner such asan optical coherence tomograph.

There are various driving systems for MEMS scanners. Among these, apiezoelectric driving system which uses the deformation of apiezoelectric body is regarded as having a higher torque density and asmaller size and obtaining a higher scan angle compared to othermethods, and is thus considered to be promising. Particularly, inapplications requiring a high displacement angle such as in a laserdisplay, resonance driving is mainly used, and at this time, the heightof a torque of the piezoelectric driving system is a great advantage.

As a piezoelectric MEMS scanner in the related art, for example, asdescribed in JP2009-2978A, there is a system in which a torsion bar isconnected to a connection part (joining part) in an actuator having astructure in which two cantilevers are connected, and the torsion bar iscaused to undergo tilt displacement by driving the cantilever inantiphase (JP2009-2978A).

In addition, as in Optical MEMS and Their Applications Conference, 2006,IEEE/LEOS International Conference on, 2006, 25-26, and Japanese Journalof Applied Physics, The Japan Society of Applied Physics, 2010, 49,04DL19, there may be cases where an actuator has a circular orelliptical shape. By causing the actuator to have such a shape, thelength of the actuator can be increased compared to a linear cantilever,so that the displacement amount can be increased. In the structures ofJP2009-2978A, Optical MEMS and Their Applications Conference, 2006.IEEE/LEOS International Conference on, 2006, 25-26, and Japanese Journalof Applied Physics, The Japan Society of Applied Physics, 2010, 49,04DL19, two plate-like actuators disposed on both sides of the rotationaxis of a mirror are provided, and the actuators are common in that baseend parts which are separated from each other in a directionperpendicular to the rotation axis are fixed.

Contrary to this, JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, Vol. 21, 6(2012), 1303-1310 proposes a structure in which two plate-like actuatorsdisposed on both sides of the rotation axis of a mirror are provided andthe actuators are fixed on the rotation axis of the mirror. Thisstructure has an advantage that a mirror tilt angle that is obtainedduring resonance driving is large because the amount of the actuatordisplaced during static driving is larger than that of the structure ofJP2009-2978A.

However, in the piezoelectric MEMS scanner having such a structure, thepiezoelectric torque cannot be efficiently converted into tiltdisplacement, and a high voltage of about 25 V is necessary to obtain asufficient displacement angle. In consideration of the durability of alead zirconate titanate (PZT) thin film, driving at about 15 V ispreferable.

In addition, in a case of an operation using the resonance driving, inorder to maintain vibration in a resonance mode, a sensor (stressdetection part) which monitors the drive displacement is necessary. Forthis, one of the actuators needs to be used as a sensor part, whichcauses a problem that the driving force significantly decreases to abouthalf.

The present invention has been made taking the foregoing circumstancesinto consideration, and an object thereof is to provide a mirror drivingdevice and a driving method thereof capable of improving a displacementefficiency compared to a structure in the related art and obtaining asufficiently large displacement angle even in a case where a sensor partis provided.

SUMMARY OF THE INVENTION

In order to achieve the above object, the following invention aspectsare provided.

A mirror driving device according to a first aspect comprises: a mirrorpart having a reflecting surface; a mirror support part which isconnected to the mirror part and supports the mirror part so as to berotatable about a rotation axis; a piezoelectric actuator part which isconnected to the mirror support part and generates a driving force torotate the mirror part about the rotation axis; and a fixing part whichsupports the piezoelectric actuator part, in which the piezoelectricactuator part includes a first actuator part and a second actuator partthat are deformed by an inverse piezoelectric effect of a piezoelectricbody caused by application of a drive voltage, the first actuator partis disposed on one side of both sides of a direction which is orthogonalto a film thickness direction of the piezoelectric body and is anorthogonal direction of the rotation axis in the orthogonal directionwhich is orthogonal to an axial direction of the rotation axis, with therotation axis interposed between the both sides in the orthogonaldirection of the rotation axis, and the second actuator part is disposedon the other side of the both sides, each of the first actuator part andthe second actuator part is connected to the mirror support part, with aconfiguration in which a first base end part, which is positioned on aside in the axial direction in the first actuator part opposite to afirst connection point that is a connection portion between the firstactuator part and the mirror support part, and a second base end part,which is positioned on a side in the axial direction in the secondactuator part opposite to a second connection point that is a connectionportion between the second actuator part and the mirror support part,are fixed to the fixing part, each of the first actuator part and thesecond actuator part is supported by the fixing part in a both-endsupported beam structure, the mirror support part is driven to be tiltedby causing the first actuator part and the second actuator part to bendin opposite directions, the upper electrodes of the first actuator partrespectively include a first electrode part and a second electrode partconstituted by a single or a plurality of electrodes, the upperelectrodes of the second actuator part respectively include a thirdelectrode part and a fourth electrode part constituted by a single or aplurality of electrodes, an arrangement of the first electrode part, thesecond electrode part, the third electrode part, and the fourthelectrode part corresponds to a stress distribution of principalstresses in an in-plane direction orthogonal to the film thicknessdirection of the piezoelectric body during resonance mode vibrationaccompanied with tilt displacement of the mirror part due to rotationabout the rotation axis, and a piezoelectric portion corresponding topositions of the first electrode part and the third electrode part and apiezoelectric portion corresponding to positions of the second electrodepart and the fourth electrode part are configured to generate stressesin opposite directions during the resonance mode vibration.

In the mirror driving device of the first aspect, since the electrodeparts are disposed in a divided form to correspond to a direction ofstress in the piezoelectric body during driving the piezoelectricactuator part (that is, during displacement), driving can be moreefficiently performed than in a configuration in the related art.

As a second aspect, in the mirror driving device of the first aspect,the first connection point and the first base end part may be in apositional relationship so as to be distant from the center of themirror part in this order in the axial direction of the rotation axis,and the second connection point and the second base end part may be in apositional relationship so as to be distant from the center of themirror part in this order in the axial direction of the rotation axis.

As a third aspect, the mirror driving device of the first aspect or thesecond aspect may further comprise: a first connection part which is amember that connects the first actuator part to the mirror support part;and a second connection part which is a member that connects the secondactuator part to the mirror support part.

As a fourth aspect, in the mirror driving device of any one of the firstto third aspects, the first actuator part and the second actuator partmay be connected to each other, and the mirror support part may beconnected to a connection portion between the first actuator part andthe second actuator part.

In a case of the fourth aspect, a form in which member elements of thefirst connection part and the second connection part described in thethird aspect are omitted is possible.

As a fifth aspect, in the mirror driving device of any one of the firstto fourth aspects, the first base end part and the second base end partmay be connected to each other.

An integral base end part shape in which the first base end part and thesecond base end part are integrated with each other can be achieved.

As a sixth aspect, in the mirror driving device of any one of the firstto fifth aspects, each of the first actuator part and the secondactuator part may be a piezoelectric unimorph actuator having alaminated structure in which a vibration plate, a lower electrode, apiezoelectric body, and an upper electrode are laminated in this order.

The structure of the piezoelectric actuator part is not limited to aunimorph structure and a bimorph structure is also possible, but aunimorph structure is the simplest configuration. Since a piezoelectricdriving system can be driven only by applying a voltage betweenelectrodes, the configuration is simple and is useful forminiaturization.

As a seventh aspect, in the mirror driving device of any one of thefirst to sixth aspects, a first mirror support part and a second mirrorsupport part, which support the mirror part from both sides in the axialdirection of the rotation axis, may be provided as the mirror supportpart.

As an eighth aspect, in the mirror driving device of any one of thefirst to seventh aspects, the first actuator part may have the firstbase end part at each of end parts on both sides in the axial direction,a movable part that extends from the first base end part at one of theend parts on both sides of the first actuator part to the first base endpart at the other thereof may have a shape bypassing the mirror part,the second actuator part may have the second base end part at each ofthe end parts on both sides in the axial direction, and a movable partthat extends from the second base end part at one of the end parts onboth sides of the second actuator part to the second base end part atthe other thereof may have a shape bypassing the mirror part.

As a ninth aspect, in the mirror driving device of any one of the firstto eighth aspects, the mirror part, the mirror support part, the firstactuator part, and the second actuator part may have a line symmetricalform with respect to the rotation axis as an axis of symmetry, in a planview in a non-driven state.

As a tenth aspect, in the mirror driving device of any one of the firstto ninth aspects, the mirror part, the mirror support part, the firstactuator part, and the second actuator part may have a line symmetricalform with respect to a center line which passes through the center ofthe mirror part and is orthogonal to the rotation axis as an axis ofsymmetry, in the plan view in the non-driven state.

As an eleventh aspect, the mirror driving device of any one of the firstto tenth aspects may further comprise: a driving circuit which applies avoltage for driving to electrodes constituting at least one electrodepart of the first electrode part or the third electrode part, andapplies a voltage for driving to electrodes constituting at least oneelectrode part of the second electrode part or the fourth electrodepart, in which a phase difference φ between a voltage waveform of thedrive voltage applied to at least one electrode part of the firstelectrode part or the third electrode part and a voltage waveform of thedrive voltage applied to at least one electrode part of the secondelectrode part or the fourth electrode part may be within the range of130°≦φ≦230°.

As a twelfth aspect, in the mirror driving device of any one of thefirst to eleventh aspects, some of the electrodes among a plurality ofelectrodes constituting the first electrode part, the second electrodepart, the third electrode part, and the fourth electrode part may be setto be at a floating potential, and a detection circuit which detects avoltage generated by a piezoelectric effect accompanied with deformationof the piezoelectric body from the electrode at the floating potentialmay be provided.

As a thirteenth aspect, the mirror driving device of any one of thefirst to twelfth aspects may further comprise: a driving circuit whichsupplies a drive voltage to the piezoelectric actuator part, in whichthe driving circuit may supply a voltage waveform of the drive voltagefor causing the mirror part to undergo resonance driving.

As a fourteenth aspect, in the mirror driving device of any one of thefirst to thirteenth aspects, the piezoelectric body used in thepiezoelectric actuator part may be a thin film having a thickness of 1to 10 μm and may be a thin film directly formed on a substrate whichserves as a vibration plate.

According to this aspect, by using a direct film formation method suchas a vapor deposition method represented by a sputtering method or asol-gel method, a piezoelectric thin film having required piezoelectricperformance can be obtained. By directly forming the piezoelectric thinfilm on a substrate and processing the resultant in a semiconductorprocess such as dry etching or wet etching, the fabrication process ofthe device can be simplified.

In a fifteenth aspect, in the mirror driving device of any one of thefirst to fourteenth aspects, the piezoelectric body used in thepiezoelectric actuator part may be one or two or more perovskite typeoxides represented by the following general formula (P-1).

General formula ABO₃  (P-1)

-   -   in the formula, A is an element in A-site and is at least one        element including Pb.

B is an element in B-site and is at least one element selected from thegroup consisting of Ti, Zr, V, Nb, Ta, Sb, Cr, Mo, W, Mn, Sc, Co, Cu,In, Sn, Ga, Zn, Cd, Fe, Mg, Si, and Ni.

O is an oxygen element.

The molar ratio among the A-site element, the B-site element, and theoxygen element is 1:1:3 as a standard, and the molar ratio may bedeviated from the reference molar ratio within a range in which aperovskite structure is able to be achieved.

As a sixteenth aspect, in the mirror driving device of any one of thefirst to fourteenth aspects, the piezoelectric body used in thepiezoelectric actuator part may be one or two or more perovskite typeoxides represented by the following general formula (P-2).

General formula A_(a)(Zr_(x),Ti_(y),M_(b-x-y))_(b)O_(c)  (P-2)

-   -   in the formula, A is an element in A-site and is at least one        element including Pb.

M is at least one element selected from the group consisting of V, Nb,Ta, and Sb. 0<x<b, 0<y<b, and 0≦b−x−y are satisfied.

a:b:c=1:1:3 is standard, and the molar ratio may be deviated from thereference molar ratio within a range in which the perovskite structureis able to be achieved.

PZT doped with an element such as Nb has a high piezoelectric constantand is thus suitable for fabrication of a device which has a small sizeand can achieve large displacement. In addition, for a piezoelectricbody used in a stress detection part, the same piezoelectric material asthat of the piezoelectric actuator part may be used.

As a seventeenth aspect, in the mirror driving device of the sixteenthaspect, the perovskite type oxide (P-2) may include Nb, and the molarratio Nb/(Zr+Ti+Nb) may be 0.06 or more and 0.20 or less.

Such a material exhibits good piezoelectric characteristics even when apolarization treatment is not performed thereon. Therefore, thepolarization treatment is unnecessary, simplification and a reduction incosts of the production process can be realized.

A mirror driving method according to an eighteenth aspect is a mirrordriving method in the mirror driving device of any one of the first toseventeenth aspects, in which a drive voltage is applied to an electrodeconstituting at least one electrode part of the first electrode part orthe third electrode part, a drive voltage is applied to an electrodeconstituting at least one electrode part of the second electrode part orthe fourth electrode part, and a phase difference φ between the drivevoltage applied to at least one electrode part of the first electrodepart or the third electrode part and the drive voltage applied to atleast one electrode part of the second electrode part or the fourthelectrode part is within the range of 130°≦φ≦2300.

In the mirror driving method according to a nineteenth aspect, some ofthe electrodes among a plurality of electrodes constituting the firstelectrode part, the second electrode part, the third electrode part, andthe fourth electrode part may be used as a detection electrode whichdetects a voltage generated by a piezoelectric effect accompanied withdeformation of the piezoelectric body, and a detection signal may beobtained from the detection electrodes during driving of the mirrorpart, in the mirror driving method of the eighteenth aspect.

For example, at least one of the frequency (driving frequency) or theamplitude of the drive voltage supplied to the piezoelectric actuatorpart can be controlled on the basis of the detection signal obtainedfrom the detection electrode. Stable resonance driving can be realizedby feeding back the detection signal to drive the piezoelectric actuatorpart.

According to the present invention, since the electrode parts aredisposed according to the distribution of the stresses generated in thepiezoelectric body during the deformation of the actuator parts, drivingcan be efficiently performed, and a larger mirror tilt angle can beobtained compared to the configuration in the related art. Furthermore,since the displacement efficiency is improved, even in a case where someof the electrodes are used for detection, a sufficient displacementangle can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating the configuration of a micromirrordevice according to a first embodiment.

FIG. 2 is a plan view illustrating another form of a mirror part.

FIG. 3 is a plan view illustrating the configuration of main parts of amicromirror device according to a second embodiment.

FIG. 4 is a schematic sectional view taken along line 4-4 of FIG. 3.

FIG. 5 is a waveform diagram showing an example of a voltage waveform.

FIG. 6 is a perspective view schematically illustrating the distributionof displacements and principal stresses of a piezoelectric body duringresonance driving.

FIG. 7 is an explanatory view schematically illustrating stressdirections in the piezoelectric body during resonance driving.

FIG. 8 is an explanatory view of a voltage application method in a casewhere all electrode parts are used as electrodes for driving in thedevice structure of FIG. 3.

FIG. 9 is an explanatory view of a form in which some of electrode partsare used for sensing in the device structure of FIG. 3.

FIG. 10 is an explanatory view of a form in which some of electrodesamong a plurality of electrodes constituting the electrode parts areused for sensing in the device structure of FIG. 3.

FIG. 11 is an explanatory view illustrating an example of dimensions ofa device of Example 1.

FIG. 12 is a plan view illustrating the configuration of main parts of amicromirror device according to Comparative Example 1.

FIG. 13 is an explanatory view of a form in which sensing is performedin the device structure of FIG. 12.

FIG. 14 is a graph showing the relationship between an applicationvoltage and an optical scan angle in Example 1 and Comparative Example1.

FIG. 15 is a graph showing the relationship between a phase differenceof a voltage waveform and a relative displacement angle.

FIG. 16 is an explanatory view of a case where four types of voltagewaveforms are used in the device structure of FIG. 8.

FIG. 17 is an explanatory view illustrating an example of a drivecontrol system in the form of FIG. 10.

FIG. 18 is a plan view illustrating the configuration of main parts of amicromirror device according to a third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments for embodying the present invention will bedescribed in detail with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a plan view illustrating a configuration of a micromirrordevice according to a first embodiment. The micromirror device 10comprises a mirror part 12, a mirror support part 14, a piezoelectricactuator part 16, and a fixing frame 18. The micromirror device 10corresponds to a form of “mirror driving device”.

The upper surface of the mirror part 12 is a reflecting surface 12C thatreflects light. A metal thin film such as Au (gold) or Al (aluminum) isformed on the reflecting surface 12C in order to increase thereflectance of incident rays. Materials and film thicknesses used formirror coating are not particularly limited, and various designs arepossible using well-known mirror materials (high reflectance materials).

The shape in the plan view of the mirror part 12 that functions as thereflecting part and the shape of the reflecting surface 12C which is amirror coated region may be coincident with each other or may bedifferent from each other. The reflecting surface 12C can be formedwithin the area range of the upper surface of the mirror part 12.Although the mirror part 12 having the reflecting surface 12C thatreflects light is described in this example, a form in which areflecting surface 12C that reflects sound waves, electromagnetic waves,or the like is implemented is also possible.

The mirror support part 14 is connected to the mirror part 12, andsupports the mirror part 12 so as to be rotatable about a rotation axisR_(A). The mirror support part 14 is constituted by a first torsion barpart 20 and a second torsion bar part 22. The first torsion bar part 20and the second torsion bar part 22 support the mirror part 12 from bothsides in the axial direction of the rotation axis R_(A) with respect tothe mirror part 12. The first torsion bar part 20 corresponds to a formof “first mirror support part”, and the second torsion bar part 22corresponds to a form of “second mirror support part”.

The piezoelectric actuator part 16 is connected to the mirror supportpart 14, and generates a driving force to rotate the mirror part 12about the rotation axis R_(A).

The fixing frame 18 is a member that supports the piezoelectric actuatorpart 16. Since the mirror part 12 is supported by the piezoelectricactuator part 16 via the mirror support part 14, the fixing frame 18functions as a member that indirectly supports the mirror part 12 viathe piezoelectric actuator part 16. In addition, in the fixing frame 18,wiring and electronic circuits (not illustrated) are provided.

Hereinafter, for convenience of description, orthogonal xyz axes areintroduced into FIG. 1 and explained. A direction normal to thereflecting surface 12C (a direction perpendicular to FIG. 1) in a casewhere the piezoelectric actuator part 16 is in a non-driven state isdefined as a z-axis direction. The z-axis direction is the filmthickness direction of a piezoelectric body in the piezoelectricactuator part 16. A direction parallel to a principal axis which is therotation axis R_(A) of the mirror part 12 rotated by the first torsionbar part 20 and the second torsion bar part 22 (horizontal directionparallel to FIG. 1) is defined as an x-axis direction. A directionorthogonal to both the x-axis and the z-axis (vertical directionparallel to FIG. 1) is defined as a y-axis direction. The x-axisdirection is the axial direction of the rotation axis R_(A) and may bereferred to as a “rotation axis direction” in some cases. The y-axisdirection is an orthogonal direction orthogonal to the axial directionof the rotation axis R_(A) and may be referred to a “rotation axisorthogonal direction” in some cases.

The micromirror device 10 has a substantially line symmetrical structure(horizontally symmetrical in FIG. 1) with respect to a center line CLwhich is parallel to the y-axis and passes through the center of themirror part 12, as an axis of symmetry. Furthermore, the micromirrordevice 10 has a substantially line symmetrical structure (verticallysymmetrical in FIG. 1) with the rotation axis R_(A) as an axis ofsymmetry.

[Shape of Mirror Part]

The mirror part 12 of this example has a rectangular shape in a planview. However, when the invention is implemented, the shape of themirror part 12 is not particularly limited. The shape is not limited tothe rectangular shape illustrated in FIG. 1, and there are variousshapes including a circular shape, an elliptical shape, a square shape,a polygonal shape, and the like. Regarding the shape of the mirror part12 in the plan view, the representation of a rectangular shape, acircular shape, an elliptical shape, a square shape, a polygonal shape,or the like is not limited to a shape based on the strict mathematicaldefinition, and means a shape that can be substantially recognized assuch a shape as an overall basic shape. For example, the concept of theterm “quadrangle” includes rectangles with chamfered corner parts, thosewith round corner parts, those in which some or all of the sides areformed as a curved line or broken line, or those in which additionalshapes necessary for connection are added to a connection portionbetween the mirror part 12 and the mirror support part 14. The same isapplied to the representation of the other shapes.

In addition, as an example of another functional shape that can beachieved by the mirror part, as described in JOURNAL OFMICROELECTROMECHANICAL SYSTEMS, Vol. 21, 6 (2012), 1303-1310, there maybe cases where a deformation prevention frame which suppresses dynamicdeformation of the reflecting surface during scan driving. For example,as illustrated in FIG. 2, as the first torsion bar part 20 and thesecond torsion bar part 22 as the mirror support part are connected to adeformation prevention frame 13 isolated from the outline of areflecting part 12D having the reflecting surface 12C, the dynamicdeformation of the reflecting surface 12C during scan driving can besignificantly reduced. In this case, the combined structure of thedeformation prevention frame 13 and the reflecting part 12D may beregarded as a “mirror part”. The mirror part in FIG. 2 is denoted byreference numeral 15. The mirror part 15 has a structure in which thefirst torsion bar part 20 and the second torsion bar part 22 areconnected to the deformation prevention frame 13 with slots 13A and 13Bformed along the outer edge of the reflecting part 12D interposedtherebetween. Instead of the mirror part 12 of FIG. 1, the mirror part15 as illustrated in FIG. 2 can be employed.

[Structure of Piezoelectric Actuator Part]

As illustrated in FIG. 1, the piezoelectric actuator part 16 comprises afirst actuator part 30 and a second actuator part 40. The first actuatorpart 30 and the second actuator part 40 are separately disposed on bothsides in the y-axis direction orthogonal to the axial direction of therotation axis R_(A), with respect to the rotation axis R_(A). The upperhalf of the piezoelectric actuator part 16 in FIG. 1 is the firstactuator part 30, and the lower half is the second actuator part 40.That is, the first actuator part 30 is disposed on one side amongregions divided by the rotation axis R_(A) into both sides (upper andlower sides in FIG. 1) with the rotation axis R_(A) in the y-axisdirection interposed therebetween, and the second actuator part 40 isdisposed on the other side. The y-axis direction corresponds to “anorthogonal direction which is a direction orthogonal to the filmthickness direction of the piezoelectric body and orthogonal to theaxial direction of the rotation axis”.

As illustrated on the left side of FIG. 1, the first actuator part 30 isconnected to one end of the first torsion bar part 20 via a connectionpart 32. The other end of the first torsion bar part 20 is connected tothe mirror part 12. In addition, as illustrated on the right side ofFIG. 1, the first actuator part 30 is connected to one end of the secondtorsion bar part 22 via a connection part 34. The other end of thesecond torsion bar part 22 is connected to the mirror part 12. Theconnection part 32 and the connection part 34 are members that connectthe first actuator part 30 to the mirror support part 14. Each of theconnection part 32 and the connection part 34 corresponds to a form of a“first connection part”. Each of the connection portion 32A between thefirst actuator part 30 and the connection part 32 and a connectionportion 34A between the first actuator part 30 and the connection part34 corresponds to a form of a “first connection point”. Otherwise, eachof the connection part 32 and the connection part 34 can be interpretedas corresponding to a form of the “first connection point”.

Each of first base end parts 36A and 36B which are base end parts onboth sides in the rotation axis direction (x-axis direction) in thefirst actuator part 30 is fixed to the fixing frame 18. The firstactuator part 30 is supported by the fixing frame 18 in a both-endsupported beam structure by a configuration in which each of the firstbase end parts 36A and 36B is fixed to the fixing frame 18. The term“both-end supported beam structure” is synonymous with “doubly supportedbeam structure”. The fixing frame 18 corresponds to a form of “fixingpart”.

The shape of the fixing frame 18 is not limited to the example of FIG.1, and various forms of designs are possible. The fixing frame 18 mayhave a function of fixing the respective base end parts of the firstactuator part 30 and the second actuator part 40. The fixing frame 18may have a configuration divided into a plurality of members.

For example, instead of the fixing frame 18 illustrated in FIG. 1, theremay be a frame structure divided into two members including a firstfixing member to which the first base end part 36A and the second baseend part 46A illustrated on the left side of FIG. 1 are fixed, and asecond fixing member to which the first base end part 36B and the secondbase end part 46B illustrated on the right side of FIG. 1 are fixed. Asanother configuration example, there may be a frame structure dividedinto two members including a first fixing member to which the first baseend parts 36A and 36B at both ends of the first actuator part 30 arefixed and a second fixing member to which the second base end parts 46Aand 46B at the both ends of the second actuator part 40 are fixed. Asstill another configuration example, there may be a frame structuredivided into four fixing members to which the first base end parts 36Aand 36B and the second base end parts 46A and 46B are respectivelyfixed.

The first base end part 36A illustrated on the left side of FIG. 1 ispositioned on the opposite side of the first actuator part 30 in thex-axis direction to the connection portion 32A for connection of theconnection part 32 to the first actuator part 30. That is, in view of arelative positional relationship between the connection portion 32A forconnection of the connection part 32 to the first actuator part 30, andthe first base end part 36A, the connection portion 32A is positioned onthe inside of the first actuator part 30, which is a side close to themirror part 12 in the x-axis direction, and the first base end part 36Ais positioned on the outside of the first actuator part 30, which is aside further away from the mirror part 12 than the connection portion32A in the x-axis direction. In other words, in the x-axis directionfrom the center of the mirror part 12, the center position of the mirrorpart 12, the connection portion 32A, and the first base end part 36A arein a positional relationship so as to gradually be distant from themirror part 12 in this order.

Similarly, the first base end part 36B illustrated on the right side ofFIG. 1 is positioned on the opposite side of the first actuator part 30in the x-axis direction to the connection portion 34A for connection ofthe connection part 34 to the first actuator part 30. That is, theconnection portion 34A for connection of the first actuator part 30 tothe connection part 34 is positioned on the inside of the first actuatorpart 30, which is the side close to the mirror part 12 in the x-axisdirection, and the first base end part 36B is positioned on the outsideof the first actuator part 30, which is the side further away from themirror part 12 than the connection portion 34A in the x-axis direction.In other words, in the x-axis direction from the center of the mirrorpart 12, the center position of the mirror part 12, the connectionportion 34A, and the first base end part 36B are in a positionalrelationship so as to gradually be distant from the mirror part 12 inthis order.

The first actuator part 30 is a piezoelectric actuator having a both endfixed type both-end supported beam structure in which each of the firstbase end parts 36A and 36B positioned on both sides in the x-axisdirection is restrained by the fixing frame 18.

Each of the first torsion bar part 20 and the second torsion bar part 22is connected to the first actuator part 30 in the vicinity of the fixedend of the first actuator part 30, that is, in the vicinity of the firstbase end parts 36A and 36B, which are root portions where the firstactuator part 30 starts to displace.

The same is applied to the second actuator part 40, and as illustratedon the left side of FIG. 1, the second actuator part 40 is connected toone end of the first torsion bar part 20 via the connection part 42. Theother end of the second torsion bar part 22 is connected to the mirrorpart 12. In addition, as illustrated on the right side of FIG. 1, thesecond actuator part 40 is connected to the second torsion bar part 22via the connection part 44. The connection part 42 and the connectionpart 44 are members that connect the second actuator part 40 to themirror support part 14. Each of the connection part 42 and theconnection part 44 corresponds to a form of “second connection part”.

Each of the connection portion 42A between the second actuator part 40and the connection part 42 and the connection portion 44A between thesecond actuator part 40 and the connection part 44 corresponds to a formof the “second connection point”. Otherwise, each of the connection part42 and the connection part 44 can be interpreted as corresponding to aform of “second connection point”.

Each of the second base end parts 46A and 46B which are base end partson both sides in the rotation axis direction (x-axis direction) in thesecond actuator part 40 is fixed to the fixing frame 18. That is, thesecond actuator part 40 is supported by the fixing frame 18 in aboth-end supported beam structure by a configuration in which each ofthe second base end parts 46A and 46B is fixed to the fixing frame 18.

The second base end part 46A illustrated on the left side of FIG. 1 ispositioned on the opposite side of the second actuator part 40 in thex-axis direction to the connection portion 42A for connection of theconnection part 42 to the second actuator part 40. That is, in view of arelative positional relationship between the connection portion 42A forconnection of the connection part 42 to the second actuator part 40, andthe second base end part 46A, the connection portion 42A is positionedon the inside of the second actuator part 40, which is the side close tothe mirror part 12 in the x-axis direction, and the second base end part46A is positioned on the outside of the second actuator part 40, whichis the side further away from the mirror part 12 than the connectionportion 42A in the x-axis direction. In other words, in the x-axisdirection from the center of the mirror part 12, the center position ofthe mirror part 12, the connection portion 42A, and the second base endpart 46A are in a positional relationship so as to gradually be distantfrom the mirror part 12 in this order.

Similarly, the second base end part 46B illustrated on the right side ofFIG. 1 is positioned on the opposite side of the second actuator part 40in the x-axis direction to the connection portion 44A for connection ofthe connection part 44 to the second actuator part 40. The connectionportion 44A for connection of the second actuator part 40 to theconnection part 44 is positioned on the inside of the second actuatorpart 40, which is the side close to the mirror part 12 in the x-axisdirection, and the second base end part 46A is positioned on the outsideof the second actuator part 40, which is the side further away from themirror part 12 than the connection portion 44A in the x-axis direction.In other words, in the x-axis direction from the center of the mirrorpart 12, the center position of the mirror part 12, the connectionportion 44A, and the second base end part 46B are in a positionalrelationship so as to gradually be distant from the mirror part 12 inthis order.

The second actuator part 40 is a piezoelectric actuator having a bothend fixed type both-end supported beam structure in which both thesecond base end parts 46A and 46B on both sides in the x-axis directionare restrained by the fixing frame 18. Each of the first torsion barpart 20 and the second torsion bar part 22 is connected to the secondactuator part 40 in the vicinity of the fixed end of the second actuatorpart 40, that is, in the vicinity of the second base end parts 46A and46B, which are root portions where the second actuator part 40 starts todisplace.

By causing the first actuator part 30 and the second actuator part 40 tobend in opposite directions, the first torsion bar part 20 and thesecond torsion bar part 22 are be moved in a direction in which theyrotate about the rotation axis R_(A), such that the mirror part 12 canbe driven to be tilted. That is, by performing driving to bend the firstactuator part 30 and the second actuator part 40 in opposite directions,the first torsion bar part 20 and the second torsion bar part 22 areinduced to undergo tilt displacement, and the mirror part 12 Is rotatedabout the rotation axis R_(A). That is, the reflecting surface 12C ofthe mirror part 12 is tilted.

<<Shape of Piezoelectric Actuator Part>>

Each of the first actuator part 30 and the second actuator part 40 inthis example has an actuator shape with a substantially semicircular arcshape in a plan view, and the two are combined to form the piezoelectricactuator part 16 having a substantially annular shape. In FIG. 1, thepiezoelectric actuator part 16 having an external shape with anelliptical ring shape slightly flattened from a true circle isillustrated. However, the actuator shape is not limited to theillustrated example. Each of the first actuator part 30 and the secondactuator part 40 may have an arcuate actuator shape along a true circleor may have an actuator shape with an elliptical arc shape having agreater oblateness than the example of FIG. 1. Here, since a highertorque can be achieved by an actuator part with a larger area, anelliptical shape is more preferable than a true circle.

<<Arrangement of Electrode Parts>>

The first actuator part 30 has, as the upper electrodes thereof, onefirst electrode part 51 and two second electrode parts 52A and 52B. Thatis, the upper electrodes of the first actuator part 30 have an electrodearrangement structure in an electrode division form divided into thefirst electrode part 51 and the second electrode parts 52A and 52B withrespect to the longitudinal direction of a beam along the shape of amovable part 38 corresponding to a portion of the beam (beam) thatconnects the one first base end part 36A and the other first base endpart 36B. The first electrode part 51 and the second electrode parts 52Aand 52B are electrodes that are independent (that is, insulated andseparated) from each other.

When a length direction along the shape of the movable part 38 from theone first base end part 36A to the other first base end part 36B in thefirst actuator part 30 is referred to as the “length direction of thefirst actuator part 30”, the first actuator part 30 has a structure inwhich the second electrode part 52A, the first electrode part 51, andthe second electrode part 52B are sequentially arranged side by sidealong the length direction of the first actuator part 30 from the leftin FIG. 1. An insulating part 55 is interposed between the secondelectrode part 52A and the first electrode part 51. An insulating part57 is interposed between the first electrode part 51 and the secondelectrode part 52B.

The second actuator part 40 has, as the upper electrodes thereof, twothird electrode parts 63A and 63B and one fourth electrode part 64. Thatis, the upper electrodes of the second actuator part 40 have anelectrode arrangement structure in an electrode division form dividedinto the third electrode parts 63A and 63B and the fourth electrode part64 with respect to the longitudinal direction of a beam along the shapeof a movable part 48 corresponding to a portion of the beam (beam) thatconnects the one second base end part 46A and the other second base endpart 46B.

The third electrode parts 63A and 63B and the fourth electrode part 64are electrodes which are independent (that is, insulated and separated)from each other. When a length direction along the shape of the movablepart 48 from the one second base end part 46A to the other second baseend part 46B in the second actuator part 40 is referred to as the“length direction of the second actuator part 40”, the second actuatorpart 40 has a structure in which the third electrode part 63A, thefourth electrode part 64, and the third electrode part 63B aresequentially arranged side by side along the length direction of thesecond actuator part 40 from the left in FIG. 1. An insulating part 65is interposed between the third electrode part 63A and the fourthelectrode part 64. An insulating part 67 is interposed between thefourth electrode part 64 and the third electrode part 63B.

Here, the electrode parts to which the same drive voltage is applied maybe connected to each other via a wiring part (not illustrated). Forexample, the electrode parts to which the same drive voltage is applied,such as a set of the two second electrode parts 52A and 52B (pair), aset of the two third electrode parts 63A and 63B, a set of the firstelectrode part 51 and the third electrode parts 63A and 63B, or a set ofthe second electrode parts 52A and 52B and the fourth electrode part 64,may be connected to each other via a wiring part (not illustrated).

Details of the arrangement of the electrodes of the first electrode part51, the second electrode parts 52A and 52B, the third electrode parts63A and 63B, and the fourth electrode part 64 in the piezoelectricactuator part 16 will be described later.

Second Embodiment

FIG. 3 is a plan view illustrating the configuration of main parts of amicromirror device according to the second embodiment. In themicromirror device 110 illustrated in FIG. 3, like elements that are thesame as or similar to those described with reference to FIG. 1 aredenoted by like reference numerals, and description thereof will beomitted. In addition, in FIG. 3, illustration of the fixing frame 18(see FIG. 1) is omitted. The micromirror device 110 corresponds to aform of “mirror driving device”.

The micromirror device 110 illustrated in FIG. 3 has a structure inwhich the first actuator part 30 and the second actuator part 40 areconnected to each other and the first base end part and the second baseend part are integrated With the micromirror device 10 of FIG. 1.

That is, the piezoelectric actuator part 16 of the micromirror device110 illustrated in FIG. 3 has an annular actuator shape in which thefirst actuator part 30 and the second actuator part 40 are connected toeach other. In addition, the mirror support part 14 is connected toconnection portions 132 and 134 of the first actuator part 30 and thesecond actuator part 40. The first torsion bar part 20 is connected tothe connection portion 132 between the first actuator part 30 and thesecond actuator part 40, and the second torsion bar part 22 is connectedto the connection portion 134 between the first actuator part 30 and thesecond actuator part 40.

In the example of FIG. 3, due to the structure in which the firstactuator part 30 and the second actuator part 40 are connected to eachother, the piezoelectric actuator part 16 having an external (outline)shape with an elliptical ring shape slightly flattened from a truecircle in a plan view is formed.

The micromirror device 110 has a simple structure in which theconnection parts 32, 34, 42, and 44 described with reference to FIG. 1are omitted, and the mirror support part 14 is directly connected theconnection portions 132 and 134 between the first actuator part 30 andthe second actuator part 40. A connection point 142 between the firsttorsion bar part 20 and the piezoelectric actuator part 16 correspondsto a form of “first connection point” and corresponds to a form of“second connection point”. Furthermore, the connection point 144 betweenthe second torsion bar part 22 and the piezoelectric actuator part 16corresponds to a form of the “first connection point” and corresponds toa form of the “second connection point”.

Furthermore, in the micromirror device 110 in FIG. 3, a single(integrated) base end part 146A in which the first base end part 36A andthe second base end part 46A described with reference to FIG. 1 areconnected to each other is formed. The base end part 146A of FIG. 3serves as the first base end part 36A described with reference to FIG.1, and serves as the second base end part 46A. The same is applied tothe base end part 146B on the right side of FIG. 3, and a single(integrated) base end part 146B in which the first base end part 36B andthe second base end part 46B described with reference to FIG. 1 areconnected to each other is formed. The base end part 146B of FIG. 3serves as the first base end part 36B described with reference to FIG.1, and serves as the second base end part 46B.

In the device structure of the second embodiment illustrated in FIG. 3,the shape of the device is simpler than that of the device structure ofthe first embodiment described with reference to FIG. 1, there is anadvantage that the manufacturing process is easy and the yield isincreased. On the other hand, as in the first embodiment described withreference to FIG. 1, the structure in which the first actuator part 30and the second actuator part 40 are separated from each other and thefirst base end part 36A and 36B of the first actuator part 30 and thesecond base end parts 46A and 46B of the second actuator part 40 areseparated from each other is also possible. By employing the structureas in the first embodiment, stress applied to each actuator part of thefirst actuator part 30 and the second actuator part 40 is reduced, andthe device can be prevented from being broken even when the tilt angleof the mirror part 12 increases.

<Structure of Piezoelectric Actuator Part>

In the following description, the structure of the second embodimenthaving a simple device shape will be described as an example. However,the same description is applied to the structure of the firstembodiment.

FIG. 4 is a schematic sectional view taken along line 4-4 of FIG. 3. Asillustrated in FIG. 4, the first actuator part 30 and the secondactuator part 40 are unimorph type thin film piezoelectric actuatorshaving laminated structure in which a lower electrode 164, apiezoelectric body 166, and an upper electrode 168 are laminated in thisorder on a silicon (Si) substrate that functions as a vibration plate160. The upper electrode 168 includes the first electrode part 51, thesecond electrode parts 52A and 52B, the third electrode parts 63A and63B, and the fourth electrode part 64. However, in FIG. 4, the secondelectrode part 52B and the third electrode part 63B are not illustrated.

A piezoelectric conversion part is formed by a laminated structure inwhich the piezoelectric body 166 is interposed between the lowerelectrode 164 and the upper electrode 168. The piezoelectric conversionpart is a portion that functions as a piezoelectric element and can alsobe expressed as the term “piezoelectric element part” or “piezoelectricactive part”. The piezoelectric conversion part can be used as a drivingpart for displacing the actuator part and can be used as a sensor part.Here, in order to simplify the description, a form in which thepiezoelectric conversion part is used as a driving part will bedescribed.

The first actuator part 30 and the second actuator part 40 function aspiezoelectric unimorph actuators which undergo bending deformation inupward and downward directions in FIG. 4 due to the inversepiezoelectric effect of the piezoelectric body 166 by applying a voltagebetween the upper electrode 168 and the lower electrode 164.

The film thickness of the respective layers illustrated in FIG. 4 andother figures and ratios thereof are drawn as appropriate forconvenience of description, and do not necessarily reflect actual filmthicknesses or ratios. In this specification, in the expression of thelaminated structure, “on” when “B is laminated on A” expresses adirection away from the surface of A in the thickness direction of thefilm as “on”. In a case where B is configured to be superimposed on theupper surface of A in a state in which A is held horizontally, “on” iscoincident with upward and downward directions when the direction ofgravity is a downward direction. However, it is also possible to tiltthe posture of A or to invert the posture upside down, and even in acase where the laminating direction of the laminated structure dependingon the posture of the substrate or the film is not necessarilycoincident with the upward and downward directions with respect to thedirection of gravity, in order to represent the vertical relationship ofthe laminated structure without confusion, the surface of a certainreference member (for example, A) is used as the reference, and adirection away from the surface in the thickness direction is expressedas “on”. In addition, the expression “B is laminated on A” is notlimited to a case where B is directly laminated on A in contact with A,and may also include a case where a single or a plurality of layers areinterposed between A and B and B is laminated on A with a single or aplurality of layers interposed therebetween.

<Description of Operation of Piezoelectric Actuator Part>

Next, the operation of the piezoelectric actuator part 16 will bedescribed. Here, in order to simplify the description, a voltagewaveform V₁₁ applied to the first electrode part 51 and a voltagewaveform V₂₁ applied to the third electrode parts 63A and 63B are set tobe the same voltage waveform V₁ (V₁₁=V₂₁=V₁), and a voltage waveform V₁₂applied to the second electrode parts 52A and 52B and a voltage waveformV₂₂ applied to the fourth electrode part 64 are set to be the samevoltage waveform V₂ (V₁₂=V₂₂=V₂). Furthermore, the voltage waveform V₁and the voltage waveform V₂ have in an antiphase relationship in which aphase difference is 180° (see FIG. 5).

FIG. 5 is a waveform diagram showing examples of the voltage waveform V₁and the voltage waveform V₂. Here, sine waveforms are illustrated asexamples of the voltage waveforms V₁ and V₂. As illustrated in FIG. 5,the voltage waveform V₁ and the voltage waveform V₂ are voltages whichare in antiphase (phase difference φ=180°) with each other, and thevoltage waveforms V₁ and V₂ which are in antiphase with each other areapplied to an electrode group of the first electrode part 51 and thethird electrode parts 63A and 63B and an electrode group of the secondelectrode parts 52A and 52B and the fourth electrode part 64, describedwith reference to FIGS. 1 to 4.

The voltage waveforms V₁ and V₂ are respectively expressed as follows.

V ₁ =V _(off1) +V _(1A) sin ωt

V ₂ =V _(off2) +V _(2A) sin(ωt+φ)

In the above expressions, V_(1A) and V_(2A) are the voltage amplitudes,ω is the angular frequency, t is the time, and φ is a phase difference.

In the example of FIG. 5, the voltage waveform which satisfiesV_(1A)=V_(2A) and φ=180° is applied. The offset voltages V_(off1) andV_(off2) are arbitrary. It is preferable to set the offset voltage suchthat, for example, V₁ and V₂ do not exceed the polarization reversalvoltage of the piezoelectric body. The polarization reversal voltage isa voltage corresponding to the coercive electric field. In FIG. 5, theoffset voltage V_(off1) for the voltage waveform V₁ and the offsetvoltage V_(off2) for the voltage waveform V₂ are the same voltage valueV_(off) (=V_(off1)=V_(off2)).

By applying the voltage waveforms V₁ and V₂ which are in antiphase asdescribed above, the first actuator part 30 and the second actuator part40 undergo bending deformation due to the inverse piezoelectric effectof the piezoelectric body 166. By causing the frequency of the voltagewaveform to be coincident with a resonance frequency corresponding to aresonance mode in which the first torsion bar part 20 and the secondtorsion bar part 22 undergo tilt displacement, the mirror part 12undergoes significant tilt displacement, and thus a wide range can bescanned.

In addition, in the example of FIG. 4, the piezoelectric layer may notbe separated (divided) in units of the electrode part and may also beused as a single sheet of (single) piezoelectric film, but when theinvention is implemented, the piezoelectric body 166 may be also dividedaccording to the division form of the electrode part. Since a portion ofthe piezoelectric body 166 interposed between the upper and lowerelectrodes functions as a driving force generating part or a stressdetection part (sensor part), unnecessary piezoelectric portions (suchas portions that do not have the upper and lower electrodes) that do notdirectly contribute to the operation of the piezoelectric conversionpart (piezoelectric element part) can be removed. By removing theunnecessary piezoelectric portions and separating the piezoelectric bodyin units of the piezoelectric conversion parts, the stiffness of theactuator part is lowered, and the actuator part can be easily deformed.

<Relationship Between Stress Distribution During Driving in ResonanceMode Vibration and Arrangement of Electrode Parts>

FIG. 6 is a perspective view schematically illustrating the displacementdistribution of the piezoelectric bodies of the first actuator part 30and the second actuator part 40 during resonance driving. In FIG. 6, aform in which the first actuator part 30 is displaced in the “+z axisdirection” and the second actuator part 40 is displaced in the “−z axisdirection”. Portions indicated by arrows B₁ and B₂ in FIG. 6 areportions with the largest actuator displacements in the z-axisdirection.

In FIG. 6, for convenience of illustration, the relative displacementamount in the z-axis direction is indicated by a difference in dotscreen pattern. In FIG. 6, regarding the denotement of the relativedisplacement amount in the z-axis direction, the maximum displacementamount (that is, the maximum value) in the +z axis direction is denotedby 100%, and the maximum displacement amount in the −z axis direction(that is, the minimum value) is denoted by −100%.

In addition, FIG. 7 schematically illustrates the distribution of thedirections of the principal stresses in the piezoelectric bodies of thefirst actuator part 30 and the second actuator part 40 during theresonance driving illustrated in FIG. 6.

In a case where the first actuator part 30 and the second actuator part40 are in the bending deformation state illustrated in FIGS. 6 and 7 ina state of being driven by the resonance mode vibration, in thepiezoelectric body 166 inside the first actuator part 30 and the secondactuator part 40, portions (reference numerals 171, 173A, and 173B) towhich stress in a tensile direction (tensile stress) is applied, andportions (reference numerals 172A, 172B, and 174 in FIG. 7) to whichstress in a compressive direction (compressive stress) is applied occur(see FIG. 6). On the basis of this stress distribution, the upperelectrodes are divided so as to correspond to the division of thepiezoelectric body regions in which stresses in opposite directions aregenerated, and each of the electrode parts (51, 63A, 63B, 52A, 52B, and64) is disposed.

The “compressive stress” and the “tensile stress” mentioned here aredefined by selecting two principal stresses in a plane substantiallyorthogonal to the film thickness direction of the piezoelectric body 166from three orthogonal principal stress vectors and determining thedirection with a higher absolute value (the direction with the maximumprincipal stress). In a case where the film thickness direction is setto the z axis, the two principal stresses in the plane substantiallyorthogonal to the film thickness direction are stresses generated in thex-y plane, and correspond to σ₁ and σ₂ in FIG. 7. Among the principalstress vectors in the x-y plane, the direction with the highestcomponent absolute value is the direction of σ₂ in FIG. 7. As a methodof denotement of the stress directions, a vector in a direction towardthe outside is defined as the tensile direction, and a vector in adirection toward the inside is defined as the compressive direction.

The reason for the above definition is that the dimensions of theactuator part are generally planar in the piezoelectric MEMS device andthe stress σ₃ in the film thickness direction can be regarded as almost0. The phrase “the dimensions are planar” means that the height issufficiently smaller than the dimension in the plane direction. The term“stresses in opposite directions” is determined on the basis of theabove definition. The plane direction of the “x-y plane” described abovecorresponds to the “in-plane direction orthogonal to the film thicknessdirection of the piezoelectric body”.

In addition, in FIG. 7, in boundary portions (reference numerals 176,177, 178, and 179) between the tensile stress regions 171, 173A, and173B which are portions where stress in the tensile direction isgenerated and the compressive stress regions 172A, 172B, and 174 whichare portions where stress in the compressive direction is generated,intermediate regions which are transitional regions in which thedirection of stress gradually (continuously) changes are present.

According to the stress distribution as illustrated in FIG. 7, the firstelectrode part 51, the second electrode parts 52A and 52B, the thirdelectrode parts 63A and 63B, and the fourth electrode part 64 arerespectively disposed on the regions (reference numerals 171, 172A,172B, 173A, 173B, and 174) of the piezoelectric parts having differentstress directions.

That is, the first electrode part 51 is provided for the tensile stressregion 171 in FIG. 7, the second electrode part 52A is provided for thecompressive stress region 172A, and the second electrode part 52B isprovided for the compressive stress region 172B. Similarly, the thirdelectrode part 63A is provided for the tensile stress region 173A, thethird electrode part 63B is provided for the tensile stress region 173B,and the fourth electrode part 64 is provided for the compressive stressregion 174. The insulating parts 55, 57, 65, and 67 (see FIG. 3) areformed to respectively correspond to the intermediate regions 176, 177,178, and 179.

The stress distribution during an operation due to resonance modevibration (resonance driving) can be analyzed by using a mode analysismethod with parameters such as device dimensions, the Young's modulus ofa material, and device shapes, which are given by using a well-knownfinite element method software. When the device is designed, the stressdistribution in the piezoelectric body at the time of driving in theresonance mode is analyzed, the regions of the upper electrodes aredivided so as to correspond to the division of the compressive stressregions and the tensile stress regions in the stress distribution on thebasis of the analysis result, and the arrangement of the first electrodepart 51, the second electrode parts 52A and 52B, the third electrodeparts 63A and 63B, and the fourth electrode part 64 is determined.

In addition, from the viewpoint of groups of the electrode partscorresponding to regions with common stress directions, the electrodeparts can be divided into two groups. The first electrode part 51 andthe third electrode parts 63A and 63B belong to a first group (firstelectrode group), the second electrode parts 52A and 52B and the fourthelectrode part 64 belong to a second group (second electrode group).

In the arrangement of the electrode parts divided as described above,the drive voltages in phase are applied to the electrode partscorresponding to the region with the same stress direction, and thedrive voltages in different phases (preferably, in antiphase) areapplied to the electrode parts corresponding to the region of differentstress directions (stresses in opposite directions). Accordingly, in themost efficient manner, a piezoelectric force can be converted into tiltdisplacement.

In the first actuator, as illustrated in FIG. 7, by arranging the firstelectrode part and the second electrode part so as to correspond toportions where the generated stress directions are different, thepiezoelectric force can be converted into displacement in the mostefficient manner. Similarly, in the second actuator, by arranging thethird electrode part and the fourth electrode part according to thegenerated stress directions, the piezoelectric force can be alsoconverted into displacement in the most efficient manner.

Furthermore, in FIGS. 3 and 4, the example in which the voltage waveformV₁ is applied to the first electrode part 51 and the third electrodeparts 63A and 63B and the voltage waveform V₂ which is in antiphase withV₁ is applied to the second electrode parts 52A and 52B and the fourthelectrode part 64 is illustrated. However, the voltage waveform V₂ mayalso applied to the first electrode part 51 and the third electrodeparts 63A and 63B and the voltage waveform V₁ may also be applied to thesecond electrode parts 52A and 52B and the fourth electrode part 64.

Furthermore, in addition to the embodiment in which all of the firstelectrode part 51, the second electrode parts 52A and 52B, the thirdelectrode parts 63A and 63B, and the fourth electrode part 64 are usedas electrodes for driving, an embodiment in which some electrode partsthereof are used as electrodes for sensing (for detection) is alsopossible. Moreover, each of the electrode parts (51, 52A, 52B, 63A. 63B,and 64) is not limited to an embodiment constituted by a singleelectrode, and at least one electrode part among the electrode parts(51, 52A, 52B, 63A, 63B, and 64) may also be constituted by a pluralityof electrodes.

<Use Form and Modification Example of Device>

Hereinafter, an example of a driving method of the micromirror deviceaccording to the embodiment of the present invention will be described.

Use Example 1

FIG. 8 shows an example in which all electrode parts of the firstelectrode part 51, the second electrode parts 52A and 52B, the thirdelectrode parts 63A and 63B, and the fourth electrode part 64 are usedas electrodes for driving. Portions of each of the electrode parts (51,52A, 52B, 63A, 63B, and 64) as the upper electrodes 168 and the lowerelectrodes 164 (see FIG. 4) with the piezoelectric body 166 interposedtherebetween each operate as a piezoelectric element part. In thisexample, all the electrode parts are used as the electrodes for driving(driving electrodes), and all the piezoelectric element parts functionas driving force generating parts.

In this case, as illustrated in FIG. 8, the same voltage waveform V₁ isapplied to the electrode group of the first electrode part 51 of thefirst actuator part 30 and the third electrode parts 63A and 63B of thesecond actuator part 40, and a voltage waveform V₂ which is in antiphasewith V₁ is applied to the electrode group of the second electrode part52A and 52B of the first actuator part 30 and the fourth electrode parts64 of the second actuator part 40. By using all of the respectivepiezoelectric element parts corresponding to the respective electrodeparts (51, 52A, 52B, 63A, 63B, and 64) as the driving force generatingparts, a large displacement angle can be realized.

It addition, the phrase “in phase” is not limited to a phase differenceof 0° and includes an allowable range of a phase difference (forexample, ±10°) that can be substantially treated as the same phase to adegree at which no problems are caused in practice. Moreover, the phrase“antiphase” is not limited to a phase difference of 180° and includes anallowable range of a phase difference (for example, 180°±10°) that canbe substantially treated as an antiphase to a degree at which noproblems are caused in practice.

For the plurality of piezoelectric element parts that function as thedriving force generating parts, in order to adjust the operationperformance between the elements, the voltage amplitude and the phasedifference of the drive voltage applied to each piezoelectric elementpart may be appropriately adjusted. A case of changing the voltageamplitude and the phase difference within the range of such adjustmentis also included in the scope of the implementation of the presentinvention.

Use Example 2

FIG. 9 shows an example in which some electrode parts of the firstelectrode part 51, the second electrode parts 52A and 52B, the thirdelectrode parts 63A and 63B, and the fourth electrode part 64 are usedto sensing (detection) electrodes for stress detection. When anelectrically open state (that is, synonymous with “open state”) is setbetween the upper electrode the lower electrode as an electrode pair ofthe piezoelectric conversion parts, stress during driving can bedetected by detecting a potential difference generated by a positivepiezoelectric effect of the piezoelectric body 166.

In FIG. 9, an example in which the second electrode parts 52A and 52Band the third electrode parts 63A and 63B are used as detectionelectrodes, and the other electrode parts are used as electrodes fordriving is illustrated.

The detection electrode is set to be at a floating potential, anddetects a voltage generated by the piezoelectric effect (positivepiezoelectric effect) of the piezoelectric body 166. In FIG. 9, theelectrodes indicated by “s₁” and “s₂” are detection electrodes forextracting a signal for sensing and represent electrodes set to be at afloating potential. Setting at the floating potential is synonymous withsetting to the electrically open state.

As described above, when some electrode parts among the plurality ofelectrode parts are used as voltage detection parts, a voltage generatedby the positive piezoelectric effect of the piezoelectric body can bedetected, and from the detected voltage signal (detection signal), thestress of the actuator part can be detected. That is, the voltagedetection part functions as a stress detection part. Accordingly, afeedback driving circuit that monitors the driven state of the mirrorpart 12 during driving of the mirror part 12 and enables the resonancestate to be maintained or the like can be configured.

As illustrated in FIG. 9, it is preferable that at least one voltagedetection part is provided for each of the actuator parts (30 and 40)constituting the piezoelectric actuator part 16. As described above, byproviding the voltage detection part for each of the actuator parts, theoperation state of each of the actuator parts can be recognized.Therefore, control on the application of an appropriate drive voltagebased on the detection signal can be achieved, and more stable resonancedriving can be realized.

Use Example 3

FIG. 10 shows an example in which each of the first electrode part 51and the fourth electrode part 64 described with reference to FIG. 8 isfurther divided into a plurality of electrodes. In FIG. 10, an examplein which the first electrode part 51 is divided into three electrodes51A, 51B, and 51C in the length direction of the first actuator part 30,and the fourth electrode part 64 is divided into three electrodes 64A,64B, and 64C in the length direction of the second actuator part 40 isillustrated.

Among the plurality of electrodes 51A to 51C constituting the firstelectrode part 51, the electrode 51B disposed at the center is used as avoltage detection part (electrode for sensing) at a floating potential,and the remaining (left and right) electrodes 51A and 51C are used asdrive voltage application parts (that is, driving force generatingparts).

Similarly, among the plurality of electrodes 64A to 64C constituting thefourth electrode part 64, the electrode 64B disposed at the center isused as a voltage detection part (electrode for sensing) at a floatingpotential and the remaining (left and right) electrodes 64A and 64C areused as drive voltage application parts (that is, driving forcegenerating parts).

Accordingly, stress detection can be achieved while minimizing theelectrode region occupied by the voltage detection parts and maintaininga high scan angle.

In FIG. 10, a form in which each of the first electrode part 51 and thefourth electrode part 64 is further divided is illustrated.Alternatively, or in combination therewith, a form in which the secondelectrode parts 52A and 52B and the third electrode parts 63A and 63Bare further divided into a plurality of electrodes is also possible. Asdescribed above, by further dividing any one of the first electrode part51 to the fourth electrode part 64, using any thereof as a stressdetection part, and using the remainder as voltage application parts,stress detection can be achieved while minimizing portions occupied bystress detection and maintaining a high scan angle.

<Production Method of Example 1>

As Example 1, a micromirror device was fabricated by the followingproduction method.

[Procedure 1] On a silicon on insulator (SOI) substrate having alaminated structure of a handle layer of 350 micrometers [μm], a boxlayer of 1 micrometer [μm], and a device layer of 24 micrometers [μm], aTi layer of 30 nanometers [nm] and an Ir layer of 150 nanometers [nm]were formed at a substrate temperature of 350° C. by a sputteringmethod. A conductive layer formed by the laminate of the Ti layer (30nm) and the Ir layer (150 nm) corresponds to the “lower electrode 164”described with reference to FIG. 4.

[Procedure 2] A piezoelectric body (PZT) layer was formed into 2.5micrometers [μm] on the substrate in which the laminate of the lowerelectrode (Ti/Ir) was formed in Procedure 1, by sing a radio frequency(RF) sputtering device.

A mixed gas of 97.5% Ar and 2.5% O₂ was used as the film formation gas,and a target material having a composition of Pb_(1.3)((Zr_(0.52)Ti_(0.4))_(0.88)Nb_(0.12))O₃ was used. The film formation pressure wasset to 2.2 millitorr [mTorr] (about 0.293 Pa), and the film formationtemperature was set to 450° C. The obtained PZT layer was an Nb-dopedPZT thin film to which Nb was added in an atomic compositional ratio of12%.

The compositional ratio of Pb contained in the formed PZT thin film wasmeasured by an X-ray fluorescence analysis (XRF) method, and the molarratio Pb/(Zr+Ti+Nb) was 1.05. That is, the chemical formula at this timeis a=1.05 with “b=1” represented inPb_(a)(Zr_(x),Ti_(y),Nb_(b-x-y))_(b)O_(c).

As described above, the ratio of the amount “a” of Pb contained in thePZT thin film having a perovskite structure that is actually obtainedcan take a value other than “1.00” due to the presence of interstitialatoms, defects, and the like. In addition, for the same reason, theratio c of O atoms can also take a value other than “3.00”.

[Procedure 3] On the substrate on which the PZT layer is formed inprocedure 2, an upper electrode having a laminated structure of Pt/Tiwas patterned by a lift-off method, pattern etching of the PZT thin filmwas performed by ICP (inductively coupled plasma) dry etching.

[Procedure 4] Thereafter, pattern etching of the device layer wasperformed by a silicon dry etching process, and the shapes of theactuator part, the mirror part, and the fixing frame were processed.

[Procedure 5] Next, the handle layer was subjected to deep reactive-ionetching (Deep RIE) from the rear surface of the substrate.

[Procedure 6] Last, the box layer was removed from the rear surface bydry etching, whereby a micromirror device having the configuration asillustrated in FIG. 3 was fabricated.

In this example, the PZT thin film was directly formed on the substrateby the sputtering method, and the dry etching was thereafter performed.As described above, by thinning the piezoelectric body, the fabricationprocess can be simplified and fine patterning can be achieved.Accordingly, the yield can be significantly improved, a furtherreduction in the size of the device can be coped with.

However, when the present invention is implemented, the piezoelectricbody of the actuator part is not limited to the thin film piezoelectricbody, and a unimorph actuator may be formed by attaching a bulkpiezoelectric body to a vibration plate or a bimorph actuator may beformed by attaching piezoelectric bodies having two different polaritiesto each other.

<Examples of Dimensions of Example 1>

As an example of the shape of the device according to Example 1,specific examples of dimensions of Example 1 are illustrated in FIG. 11.For the dimensions a to g illustrated in FIG. 11, a=0.05 mm, b=1.0 mm,c=4.0 mm, d=1.32 mm, e=2.96 mm, f=0.08 mm, and g=0.48 mm are given. Atthis time, the resonance frequency of a resonance mode used for scanningis around 3400 Hz.

The dimension a is the length in the x-axis direction of the base endparts (164A and 164B). The dimension b is the width dimension in thex-axis direction of the beam (beam) portions in the actuator parts (30and 40). The dimension c is the length in the x-axis direction of thetorsion bar parts (20 and 22). The dimension d is the width dimension inthe x-axis direction of the mirror part 12. The dimension e is thelength of the mirror part 12 in the y-axis direction. The dimension f isthe width dimension in the y-axis direction of the torsion bar parts (20and 22). The dimension g is the width dimension in the y-axis directionof the base end parts (146A and 146B).

Comparative Example 1

A micromirror device according to Comparative Example 1 as illustratedin FIG. 12 was fabricated using exactly the same substrate (SOIsubstrate) and production process method as those in Example 1.

In the device 210 illustrated in FIG. 12, like elements that are thesame as or similar to those described with reference to FIG. 3 aredenoted by like reference numerals, and description thereof will beomitted. The device 210 of Comparative Example 1 illustrated in FIG. 12has a structure in which the upper electrodes of the first actuator part30 and the second actuator part 40 have only a single electrode part 251and a single electrode part 264, respectively. FIG. 12 shows an examplein which these two electrode parts 251 and 264 are used as electrodesfor driving. A voltage waveform V₁ may be applied to the electrode part251 of the first actuator part 30, and a voltage waveform V₂ which is inantiphase with V₁ may be applied to the electrode part 264 of the secondactuator part 40.

In a case of where stress detection is performed in the device formillustrated in FIG. 12, as illustrated in FIG. 13, any one electrodepart of the two electrode parts 251 and 264 is used for detection(sensing). FIG. 13 shows an example in which the electrode part 264 ofthe second actuator part 40 is used for sensing. The electrode part 264used for sensing is set to be at a floating potential and detects avoltage generated by a positive piezoelectric effect of thepiezoelectric body. In FIG. 13, the electrode indicated by “s” is adetection electrode for extracting a signal for sensing and representsan electrode set to be at a floating potential.

<Evaluation Experiment on Operation of Device>

An experiment was conducted to compare the operation performance of thedevice fabricated in Example 1 and the device fabricated in ComparativeExample 1. FIG. 14 is a graph showing the relationship between the drivevoltage and the scan angle in the device as an experiment subject.

As experiment subjects, four types of devices, “Example 1 (drivingonly)”, “Example 1 (with angle sensing)”, “Comparative Example 1(driving only)”, and “Comparative Example 1 (with angle sensing)evaluated. “Example 1 (driving only)”, “Example 1 (with angle sensing)”,“Comparative Example 1 (driving only)”, and “Comparative Example 1 (withangle sensing) respectively correspond to forms of FIGS. 8, 9, 12, and13.

Furthermore, the dimensions of the device are all exemplified in FIG.11.

The voltage waveforms V₁ and V₂ in a sine wave having a voltageamplitude V_(PP) are input to the electrode parts for driving in eachdevice to induce resonance vibration accompanied with the rotationalmotion of the mirror part 12, and the mechanical deflection angle of themirror part 12 was measured at a laser scan angle. Regarding a method ofapplying the drive voltage, the devices of “Example 1 (driving only)”and “Example 1 (with angle sensing)” conform to the illustration ofFIGS. 8 and 9, respectively. The devices of “Comparative Example 1(driving only)” and “Comparative Example 1 (with angle sensing)” conformto the illustration of FIGS. 12 and 13, respectively.

The results of the experiment are shown in FIG. 14. In FIG. 14, thehorizontal axis represents the voltage amplitude (in units of volts[V]), and the vertical axis represents the optical scan angle (in unitsof degrees [deg]).

As is apparent from FIG. 14, the device of Example 1 including aplurality of electrode parts in a single actuator part has a higher scanangle than that of the device of Comparative Example 1. In addition,even in a case where a stress detection part which uses some of theelectrode parts for sensing was provided, it was confirmed that thedevice of Example 1 can maintain a higher scan angle than that of thedevice of Comparative Example 1.

<Piezoelectric Material>

A piezoelectric body suitable for this embodiment may be a bodyincluding one or two or more perovskite type oxides represented by thefollowing general formula (P-1).

General formula ABO₃  (P-1)

-   -   In the formula, A is an element in A-site and is at least one        element including Pb.

B is an element in B-site and is at least one element selected from thegroup consisting of Ti, Zr, V, Nb, Ta, Sb, Cr, Mo, W, Mn, Sc, Co, Cu,In, Sn, Ga, Zn, Cd, Fe, Mg, Si, and Ni.

O is an oxygen element.

The molar ratio between the A-site element, the B-site element, and theoxygen element is 1:1:3 as a standard, and the molar ratio may also bedeviated from the reference molar ratio within a range in which theperovskite structure can be achieved.

The perovskite type oxides represented by the above general formula(P-1) include: lead-containing compounds such as lead titanate, leadzirconate titanate (PZT), lead zirconate, lanthanum lead titanate, leadlanthanum zirconate titanate, lead magnesium niobate-lead zirconatetitanate, lead nickel niobate-lead zirconate titanate, and lead zincniobate-lead zirconate titanate and mixed crystal systems thereof, andlead-free compounds such as barium titanate, strontium barium titanate,sodium bismuth titanate, bismuth potassium titanate, sodium niobate,potassium niobate, lithium niobate, and bismuth ferrite and mixedcrystal systems thereof.

In addition, the piezoelectric film of this embodiment preferablyincludes one or two or more perovskite type oxides (P-2) represented bythe following general formula (P-2).

General formula A_(a)(Zr_(x),Ti_(y),M_(b-x-y))_(b)O_(c)  (P-2)

-   -   In the formula, A is an element in A-site and is at least one        element including Pb.

M is at least one element selected from the group consisting of V, Nb,Ta, and Sb.

0<x<b, 0<y<b, and 0≦b−x−y are satisfied.

a:b:c=1:1:3 is standard, and the molar ratio may be deviated from thereference molar ratio within a range in which the perovskite structurecan be achieved.

The perovskite type oxide (P-2) is an oxide in which a part of theB-site of intrinsic PZT or PZT is substituted with M. It is known thatin the PZT to which various donor ions having a valence higher than thevalence of the substituted ion are added, characteristics such aspiezoelectric performance are improved compared to the intrinsic PZT. Itis preferable that M is one or two or more donor ions having a valencehigher than that of tetravalent Zr or Ti. As such donor ions, there areV⁵⁺, Nb⁵⁺, Ta⁵⁺, Sb⁵⁺, Mo⁶⁺, and W⁶⁺.

The range of b−x−y is not particularly limited as long as the perovskitestructure can be achieved. For example, in a case where M is Nb, themolar ratio Nb/(Zr+Ti+Nb) is preferably 0.05 or more and 0.25 or less,and more preferably 0.06 or more and 0.20 or less.

Since a piezoelectric film made of the perovskite type oxidesrepresented by the above general formulas (P-1) and (P-2) has a highpiezoelectric strain constant (d31 constant), a piezoelectric actuatorcomprising the piezoelectric film has excellent displacementcharacteristics.

Furthermore, the piezoelectric actuator comprising the piezoelectricfilm made of the perovskite type oxides represented by the generalformulas (P-1) and (P-2) has voltage-displacement characteristics withexcellent linearity. These piezoelectric materials exhibit good actuatorcharacteristics and sensor characteristics when the present invention isimplemented. In addition, the perovskite type oxide represented by thegeneral formula (P-2) has a higher piezoelectric constant than thatrepresented by the general formula (P-1).

As a specific example of the piezoelectric body in this embodiment, forexample, a lead zirconate titanate (PZT) thin film doped with Nb in anatomic composition percentage of 12% may be used. By forming a film ofPZT doped with 12% Nb by a sputtering method or the like, a thin filmhaving piezoelectric characteristics as high as a piezoelectric constantof d31=250 μm/V can be stably fabricated.

In addition, in this example, PZT is selected as the piezoelectricmaterial used for the actuator part (the driving force generating partand the stress detection part), but the piezoelectric material does notneed to be limited to this material. For example, a lead-freepiezoelectric body such as BaTiO₃, KNaNbO₃, or BiFeO₃ may be used, and anon-perovskite piezoelectric body such as AlN and ZnO₂ may also be used.

<Film Formation Method>

A vapor deposition method is preferable as the film formation method ofthe piezoelectric body. For example, in addition to the sputteringmethod, various methods such as an ion plating method, a metal organicchemical vapor deposition (MOCVD) method, and a pulse laser deposition(PLD) method may be applied. It is also conceivable to use a methodother than the vapor deposition method (for example, sol-gel method). Aconfiguration in which a piezoelectric thin film is directly formed on asubstrate by a vapor deposition method or a sol-gel method ispreferable. In particular, the piezoelectric body 166 of this embodimentis preferably a thin film having a film thickness of 1 μm or more and 10μm or less.

<Waveforms of Drive Voltages>

In Example 1 described above, as illustrated in FIG. 5, although thevoltage waveforms V₁ and V₂ of the drive voltages are set to be inantiphase (phase difference φ=180°), the phase difference therebetweenmay be shifted to some extent from 180°. For example, in a case where acomponent (noise vibration) other than the intended resonance vibrationoccurs, there may be cases where the phase difference between V₁ and V₂is shifted from 180° by a small amount in order to eliminate thiscomponent.

FIG. 15 shows the relationship between the phase difference between V₁and V₂ and the relative displacement angle. The displacement angle isthe maximum when the phase difference between V₁ and V₂ is 180° (inantiphase with each other) and is the minimum when the phase differenceis 0° (in phase with each other). In order to obtain the sufficientdisplacement angle, typically, the phase difference is preferably withina range of 90°≦φ≦270°. Moreover, the phase difference is more preferablywithin a range of 130°≦φ≦230°.

When the present invention is implemented, the types of the drivewaveforms may be two or more types. For example, as illustrated in FIG.16, the voltage waveform applied to the first electrode part 51 may beset to V₁₁, the voltage waveform applied to the second electrode parts52A and 52B may be set to V₁₂, the voltage waveform applied to the thirdelectrode parts 63A and 63B may be set to V₂₁, and the voltage waveformapplied to the fourth electrode part 64 may be set to V₂₂.

As these four types of drive voltages, for example, the followingwaveforms may be used.

V ₁₁ =V _(off11) +V _(11A) sin ωt

V ₁₂ =V _(off12) +V _(12A) sin(ωt+φ)

V ₂₁ =V _(off21) +V _(21A) sin ωt

V ₂₂ =V _(off22) +V _(22A) sin(ωt+φ)

In the expressions, each of V_(11A), V_(12A), V_(21A), and V_(22A) isthe voltage amplitude, ω is the angular frequency, t is the time, and φis the phase difference. The phase difference φ is within a range of90°≦φ≦270°, and more preferably within a range of 130°≦φ≦230°.

V_(11A), V_(12A), V_(21A), and V_(22A) may have an arbitrary value of 0or more. All of V_(11A), V_(12A), V_(21A), and V_(22A) may be set todifferent values, or some or all thereof may also be set to the samevalue. In addition, in the above expressions, the phases of V₁₁ and V₂₁are coincident with each other, and the phases of V₁₂ and V₂₂ arecoincident with each other. However, these phases do not need to becompletely coincident with each other, and a slight phase shift of about±10° is acceptable.

Furthermore, the application voltage is not limited to a sine wave, andperiodic waveforms such as a square wave and a triangular wave may alsobe applied thereto.

<Drive Voltage Supplying Means (Driving Control Part)>

FIG. 17 is a diagram illustrating an example of the configuration of acontrol system used for driving a device. Here, the control system ofthe device form shown in FIG. 10 is illustrated. In the case of thedevice form described with reference to FIG. 10, as illustrated in FIG.17, the electrodes 51A and 51C in the first electrode part 51 and thesecond electrode parts 52A and 52B in the first actuator part 30 usedfor driving, and the third electrode parts 63A and 63B and theelectrodes 64A and 64C of and the fourth electrode part 64 in the secondactuator part 40 are connected to the corresponding voltage outputterminals of a driving circuit 310. The voltage waveform V₁ for drivingis supplied from the driving circuit 310 to the electrodes 51A and 51Cin the first electrode part 51 of the first actuator part 30 and thethird electrode parts 63A and 63B of the second actuator part 40.

The voltage waveform V₂ for driving is supplied from the driving circuit310 to the second electrode parts 52A and 52B of the first actuator part30 and the electrodes 64A and 64C in the fourth electrode part 64 of thesecond actuator part 40. In addition, in FIG. 17, although the electrodeparts to which the same drive voltage is applied are connected inparallel, a configuration in which drive voltages are individuallysupplied to the electrode parts may also be employed.

The driving circuit 310 supplies the voltage waveforms V₁ and V₂ of thedrive voltage for causing the mirror part 12 to undergo resonancedriving at near the resonance frequency fx of the resonance mode inwhich the mirror part 12 (see FIG. 3) performs rotational motion aboutthe rotation axis R_(A). During the resonance driving, the displacementamount reaches the highest value when the frequency of the drive voltageis caused to be completely coincident with the resonance frequency ofthe device. However, in this case, there are also disadvantage that ittakes time to stabilize the vibration, the displacement amount greatlydecreases when the resonance frequency slightly changes due to theinfluence of temperature and the like. In consideration of this, theremay be cases where driving is performed at a frequency slightly shiftedfrom the resonance frequency within a range where a necessarydisplacement amount can be secured. “Near the resonance frequency fx”has a meaning including a frequency coincident with the resonancefrequency fx and a frequency slightly shifted from the resonancefrequency fx within a range in which a necessary displacement amount canbe secured.

Each of the electrode 51B of the first actuator part 30 and theelectrode part 64B of the second actuator part 40, which are used forsensing, is connected to a detection circuit 312. The lower electrode164 is connected to the common terminal (V₀ terminal, for example,ground terminal) of the driving circuit 310 or the detection circuit312. Each electrode is connected to the driving circuit 310 or thedetection circuit 312 via a wiring member such as wire bonding or apattern wiring part on a substrate (not illustrated).

A voltage signal is detected from the electrode 51B and the electrodepart 64B for sensing via the detection circuit 312, and the detectionresults are notified to a control circuit 314. On the basis of thesignal obtained from the detection circuit 312, the control circuit 314sends a control signal to the driving circuit 310 so as to maintainresonance and controls the application of the drive voltages to thefirst actuator part 30 and the second actuator part 40.

For example, feedback is applied to the driving circuit 310 so as tomaintain resonance so that the phases of the waveform of the drivevoltage applied to the piezoelectric actuator parts and the waveformdetected from the stress detection part (sensor part) have predeterminedvalues. The control circuit 314 controls the voltage or drivingfrequency applied to the piezoelectric actuator part based on thedetection signal obtained from the stress detection part of the mirrorpart 12.

Such a feedback control circuit may be embedded in the detection circuit312. In addition, the driving circuit 310, the detection circuit 312,and the control circuit 314 may be collectively configured as anintegrated circuit such as an application specific integrated circuit(ASIC).

Operational Effects of Embodiment

According to the above-described embodiment, since the electrode partsare arranged according to the stress distribution generated in thepiezoelectric bodies at the time of deformation of the actuator parts,the actuator parts can be efficiently driven, and compared to theconfiguration in the related art, a larger mirror tilt angle can beobtained.

Furthermore, according to the embodiment of the present invention, sincethe displacement efficiency is improved compared to the configuration inthe related art, even in a case where some of the electrodes are usedfor stress detection, a sufficient displacement angle can be obtained.

<Another Example of Form of Piezoelectric Actuator Part>

FIG. 18 is a plan view illustrating the configuration of main parts of amicromirror device according to a third embodiment. In a micromirrordevice 410 illustrated in FIG. 18, like elements that are the same as orsimilar to those described with reference to FIG. 1 are denoted by likereference numerals, and description thereof will be omitted. Inaddition, in FIG. 18, illustration of the fixing frame 18 (see FIG. 1)is omitted. The micromirror device 410 corresponds to a form of “mirrordriving device”.

In the first actuator part 30 of the micromirror device 410 illustratedin FIG. 18, the movable part 38 that connects the first base end parts36A and 36B, which are end parts on both sides in the x-axis direction,has a shape along three sides corresponding to the upper base and thetwo legs of a substantially isosceles trapezoid. Similarly, in thesecond actuator part 40 of the micromirror device 410, the movable part48 that connects the second base end parts 46A and 46B, which are endparts on both sides in the x-axis direction, has a shape along threesides corresponding to the upper base and the two legs of asubstantially isosceles trapezoid.

The first actuator part 30 and the second actuator part 40 having theactuator shape as illustrated in FIG. 18 may be employed.

As the actuator shapes of the first actuator part 30 and the secondactuator part 40, various forms are possible. As illustrated in FIGS. 1,3, and 18, various forms of a configuration in which the movable part 38that extends from the one first base end part 36A of the base end partson both sides in the x-axis direction in the first actuator part 30 tothe other first base end part 36B has a shape bypassing the mirror part12, and the movable part 48 that extends from the one second base endpart 46A of the base end parts on both sides in the x-axis direction inthe second actuator part 40 to the other second base end part 46B has ashape bypassing the mirror part 12 can be designed.

<Modification Example of Mirror Support Part>

In the above-described embodiment, the first torsion bar part 20 and thesecond torsion bar part 22 are connected to positions coincident withthe rotation axis R_(A) of the mirror part 12, and are formed to extendin the axial direction of the rotation axis R_(A) toward the outside ofthe mirror part 12. In addition, FIG. 3 illustrates an example in whichthe first torsion bar part 20 and the second torsion bar part 22 areconnected to the positions coincident with the rotation axis R_(A) ofthe mirror part 12. However, the connection positions of the torsion barparts may not be strictly coincident with the rotation axis R_(A), andthe torsion bar parts are not necessarily limited to a form ofconnection to a single point, and may be connected to a plurality ofpoints.

For example, in a case where the substantially center portion in thelongitudinal direction of the mirror part 12 (not limited to the truecenter point on design but the vicinity thereof) is the rotation axisR_(A), in addition to an embodiment in which a torsion bar is connectedto and is supported by a single point at the position substantiallycoincident with the rotation axis R_(A), a structure in which torsionbars are connected at positions of two or more points in axial symmetrywith respect to the position of the rotation axis R_(A) interposedtherebetween within a range in which the position can be regarded as thesubstantially center portion, is also possible.

Application Example

The mirror driving device of the present invention can be used invarious applications as an optical device that reflects light such aslaser light and changes the traveling direction of light. For example,the mirror driving device can be widely applied to an optical deflector,an optical scanning device, a laser printer, a barcode reader, a displaydevice, various optical sensors (distance-measuring sensors and shapemeasurement sensors), an optical communication device, a laserprojector, an optical coherence tomography diagnostic device, and thelike. Furthermore, the present invention is not limited to theapplications in which light is reflected, and can also be applied to amirror device in applications in which sound waves are reflected.

In addition, the present invention is not limited to the above-describedembodiments, and many modifications are possible by those with ordinaryskill in the art within technical scope of the present invention.

EXPLANATION OF REFERENCES

-   -   10: micromirror device    -   12: mirror part    -   12C: reflecting surface    -   13: deformation prevention frame    -   14: mirror support part    -   15: mirror part    -   16: piezoelectric actuator part    -   18: fixing frame    -   20: first torsion bar part    -   22: second torsion bar part    -   30: first actuator part    -   32, 34: connection part    -   32A, 34A: connection portion    -   36A, 36B: first base end part    -   38: movable part    -   40: second actuator part    -   42, 44: connection part    -   42A, 44A: connection portion    -   46A, 46B: second base end part    -   48: movable part    -   51: first electrode part    -   52A, 52B: second electrode part    -   63A, 63B: third electrode part    -   64: fourth electrode part    -   110: micromirror device    -   132, 134: connection portion    -   142: connection point    -   144: connection point    -   160: vibration plate    -   164: lower electrode    -   166: piezoelectric body    -   168: upper electrode    -   310: driving circuit    -   312: detection circuit    -   314: control circuit    -   410: micromirror device

What is claimed is:
 1. A mirror driving device comprising: a mirror parthaving a reflecting surface; a mirror support part which is connected tothe mirror part and supports the mirror part so as to be rotatable abouta rotation axis; a piezoelectric actuator part which is connected to themirror support part and generates a driving force to rotate the mirrorpart about the rotation axis; and a fixing part which supports thepiezoelectric actuator part, wherein the piezoelectric actuator partincludes a first actuator part and a second actuator part which aredeformed by an inverse piezoelectric effect of a piezoelectric bodycaused by application of a drive voltage, the first actuator part isdisposed on one side of both sides of a direction which is orthogonal toa film thickness direction of the piezoelectric body and is anorthogonal direction of the rotation axis in the orthogonal directionwhich is orthogonal to an axial direction of the rotation axis, with therotation axis interposed between the both sides in the orthogonaldirection of the rotation axis, and the second actuator part is disposedon the other side of the both sides, each of the first actuator part andthe second actuator part is connected to the mirror support part, with aconfiguration in which a first base end part, which is positioned on aside in the axial direction in the first actuator part opposite to afirst connection point that is a connection portion between the firstactuator part and the mirror support part, and a second base end part,which is positioned on a side in the axial direction in the secondactuator part opposite to a second connection point that is a connectionportion between the second actuator part and the mirror support part,are fixed to the fixing part, each of the first actuator part and thesecond actuator part is supported by the fixing part in a both-endsupported beam structure, the first actuator part has the first base endpart at each of end parts on both sides in the axial direction, amovable part that extends from the first base end part at one of the endparts on both sides of the first actuator part to the first base endpart at the other thereof has a shape bypassing the mirror part, thesecond actuator part has the second base end part at each of the endparts on both sides in the axial direction, a movable part that extendsfrom the second base end part at one of the end parts on both sides ofthe second actuator part to the second base end part at the otherthereof has a shape bypassing the mirror part, the first base end partand the second base end part are separated from each other, the mirrorsupport part is driven to be tilted by causing the first actuator partand the second actuator part to bend in opposite directions, the upperelectrodes of the first actuator part respectively include a firstelectrode part and a second electrode part constituted by a single or aplurality of electrodes, the upper electrodes of the second actuatorpart respectively include a third electrode part and a fourth electrodepart constituted by a single or a plurality of electrodes, anarrangement of the first electrode part, the second electrode part, thethird electrode part, and the fourth electrode part corresponds to astress distribution of principal stresses in an in-plane directionorthogonal to the film thickness direction of the piezoelectric bodyduring resonance mode vibration accompanied with tilt displacement ofthe mirror part due to rotation about the rotation axis, and apiezoelectric portion corresponding to positions of the first electrodepart and the third electrode part and a piezoelectric portioncorresponding to positions of the second electrode part and the fourthelectrode part are configured to generate stresses in oppositedirections during the resonance mode vibration.
 2. The mirror drivingdevice according to claim 1, wherein the first connection point and thefirst base end part are in a positional relationship so as to be distantfrom the center of the mirror part in this order in the axial directionof the rotation axis, and the second connection point and the secondbase end part are in a positional relationship so as to be distant fromthe center of the mirror part in this order in the axial direction ofthe rotation axis.
 3. The mirror driving device according to claim 1,further comprising: a first connection part which is a member thatconnects the first actuator part to the mirror support part; and asecond connection part which is a member that connects the secondactuator part to the mirror support part.
 4. The mirror driving deviceaccording to claim 1, wherein the first actuator part and the secondactuator part are connected to each other, and the mirror support partis connected to a connection portion between the first actuator part andthe second actuator part.
 5. The mirror driving device according toclaim 1, wherein each of the first electrode part, the second electrodepart, the third electrode part and the fourth electrode part is used asan electrode for driving that applies a voltage for driving, at leastone electrode of the first electrode part, the second electrode part,the third electrode part and the fourth electrode part is divided into aplurality of electrodes, and some of the plurality of electrodes areused as electrodes for detection that detect a voltage generated by apiezoelectric effect due to a deformation of the piezoelectric body. 6.The mirror driving device according to claim 1, wherein each of thefirst actuator part and the second actuator part is a piezoelectricunimorph actuator having a laminated structure in which a vibrationplate, a lower electrode, a piezoelectric body, and an upper electrodeare laminated in this order.
 7. The mirror driving device according toclaim 1, wherein a first mirror support part and a second mirror supportpart, which support the mirror part from both sides in the axialdirection of the rotation axis, are provided as the mirror support part.8. The mirror driving device according to claim 1, wherein the mirrorpart, the mirror support part, the first actuator part, and the secondactuator part have a line symmetrical form with respect to the rotationaxis as an axis of symmetry, in a plan view in a non-driven state. 9.The mirror driving device according to claim 1, wherein the mirror part,the mirror support part, the first actuator part, and the secondactuator part have a line symmetrical form with respect to a center linewhich passes through the center of the mirror part and is orthogonal tothe rotation axis as an axis of symmetry, in the plan view in thenon-driven state.
 10. The mirror driving device according to claim 1,further comprising a driving circuit which applies a voltage for drivingto electrodes constituting at least one electrode part of the firstelectrode part or the third electrode part, and applies a voltage fordriving to electrodes constituting at least one electrode part of thesecond electrode part or the fourth electrode part, wherein a phasedifference φ between the drive voltage applied to at least one electrodepart of the first electrode part or the third electrode part and thedrive voltage applied to at least one electrode part of the secondelectrode part or the fourth electrode part is within the range of130°≦φ≦230°.
 11. The mirror driving device according to claim 1, whereinsome of the electrodes among a plurality of electrodes constituting thefirst electrode part, the second electrode part, the third electrodepart, and the fourth electrode part are set to be at a floatingpotential, and a detection circuit which detects a voltage generated bya piezoelectric effect accompanied with deformation of the piezoelectricbody from the electrode at the floating potential is provided.
 12. Themirror driving device according to claim 1, further comprising a drivingcircuit which supplies a drive voltage to the piezoelectric actuatorpart and supplies a voltage waveform of the drive voltage for causingthe mirror part to undergo resonance driving.
 13. The mirror drivingdevice according to claim 1, wherein the piezoelectric body used in thepiezoelectric actuator part is a thin film having a thickness of 1 to 10μm and is a thin film directly formed on a substrate which serves as avibration plate.
 14. The mirror driving device according to claim 1,wherein the piezoelectric body used in the piezoelectric actuator partis one or two or more perovskite type oxides represented by thefollowing general formula (P-1),General formula ABO₃  (P-1) in the formula, A is an element in A-siteand is at least one element including Pb, B is an element in B-site andis at least one element selected from the group consisting of Ti, Zr, V,Nb, Ta, Sb, Cr, Mo, W, Mn, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, Mg, Si,and Ni, O is an oxygen element, and the molar ratio among the A-siteelement, the B-site element, and the oxygen element is 1:1:3 as astandard, and the molar ratio may be deviated from the reference molarratio within a range in which a perovskite structure is able to beachieved.
 15. The mirror driving device according to claim 1, whereinthe piezoelectric body used in the piezoelectric actuator part is one ortwo or more perovskite type oxides represented by the following generalformula (P-2),General formula A_(a)(Zr_(x),Ti_(y),M_(b-x-y))_(b)O_(c)  (P-2) in theformula, A is an element in A-site and is at least one element includingPb, M is at least one element selected from the group consisting of V,Nb, Ta, and Sb, 0<x<b, 0<y<b, and 0≦b−x−y are satisfied, and a:b:c=1:1:3is standard, and the molar ratio may be deviated from the referencemolar ratio within a range in which the perovskite structure is able tobe achieved.
 16. The mirror driving device according to claim 15,wherein the perovskite type oxide (P-2) includes Nb, and the molar ratioNb/(Zr+Ti+Nb) is 0.06 or more and 0.20 or less.
 17. A mirror drivingmethod in the mirror driving device according to claim 1, wherein adrive voltage is applied to an electrode constituting at least oneelectrode part of the first electrode part or the third electrode part,a drive voltage is applied to an electrode constituting at least oneelectrode part of the second electrode part or the fourth electrodepart, and a phase difference φ between the drive voltage applied to atleast one electrode part of the first electrode part or the thirdelectrode part and the drive voltage applied to at least one electrodepart of the second electrode part or the fourth electrode part is withinthe range of 130°≦φ≦230°.
 18. The mirror driving method according toclaim 17, wherein some of the electrodes among a plurality of electrodesconstituting the first electrode part, the second electrode part, thethird electrode part, and the fourth electrode part are used as adetection electrode which detects a voltage generated by a piezoelectriceffect accompanied with deformation of the piezoelectric body, adetection signal is obtained from the detection electrodes duringdriving of the mirror part.